recommendation for OIL-fired condensing boiler?

[shagty]

hi everyone

i'd be grateful for your recommendations on oil fired condensing boilers and pipework arrangement to facilitate HWS priority control. the application is a dwelling where the boiler output is based on space heating load at about 18kW. the existing heating scheme is an open vented dual system and comprises a solid fuel stove and oil boiler. the proposed piping configuration is S-plan with three zones: 2 HTG and 1 HWS. the boiler room is isolated from the house and includes a conventional flue.

the question on piping layout concerns priority hot water control for the oil boiler. Q.1 is a 3 port divert valve be required to achieve HWS priority control and Q.2 if a 3 port diverter valve is necessary, can the heating line of the 3 port valve be hooked up to the solid fuel in parallel, before two zoned sub circuits?
some desirable boiler features include:
fully modulating
weather compensation
how water priority
quite operation

reliability and efficiency are key factors as well.

any help/advice would be greatly appreciated

thanks for reading

best regards

s

 

[DeltaT2]

hi everyone

i'd be grateful for your recommendations on oil fired condensing boilers and pipework arrangement to facilitate HWS priority control. the application is a dwelling where the boiler output is based on space heating load at about 18kW. the existing heating scheme is an open vented dual system and comprises a solid fuel stove and oil boiler. the proposed piping configuration is S-plan with three zones: 2 HTG and 1 HWS. the boiler room is isolated from the house and includes a conventional flue.

the question on piping layout concerns priority hot water control for the oil boiler. Q.1 is a 3 port divert valve be required to achieve HWS priority control and Q.2 if a 3 port diverter valve is necessary, can the heating line of the 3 port valve be hooked up to the solid fuel in parallel, before two zoned sub circuits?
some desirable boiler features include:
fully modulating
weather compensation
how water priority
quite operation

reliability and efficiency are key factors as well.

any help/advice would be greatly appreciated

thanks for reading

best regards

s

For an optimum, you need to feed both boilers into a neutral point in the system, something like a Dunsley Baker Neutralizer are the simplest things to use, minimum controls etc. There is many other ways of doing it, thermal stores etc.

As for oil boilers; we use the Firebird range, they are manufactured in Eire & are great wee boilers.
HTH

 

[outinthestix]

AFIK there isn't a modulating oil boiler available.
I agree with Delta T2 about pipework arrangements but would usually fit Grant boilers given the choice, although Firebirds heat only offerings seem ok. Stix.

 

[dcawkwell]

If you are wanting to use two boilers I suggest a heat store with twin
coils. Both boilers can heat this. The heat store then supplies the central
heating and hot water. Or you can have a heat store that will heat a
separate hot water tank.

I've used warmflow and grant.
Both seem to be reliable.

 

[shagty]

thanks for all your suggestions, they will be very helpful

coming back to the proposed piping arrangement for the oil side, i would like to implement a control whereby the space heating and DHW can not be heated simultaneously, with hot water taking priority. Im considering a 3-port diverter valve for this and 2-port valves downstream for zoning the space heating. i've attached a sketch which illustrates this proposal and would be grateful for your thoughts.

the existing system in this bungalow actually contains a high output back boiler (soon to be replaced with a stove), connected to a dual coil cylinder via 28mm pipes. the boiler and cylinder are about 8 metres apart with a hallway in between. the gravity flow presently rises from boiler to attic and drops to the cylinder, before returning through the floor screed back to the boiler. the cylinder coil is above the boiler but heat transfer is very poor.
I haven't seen enough of these loops working satisfactorily to retain it. therefore i'm thinking of using a vented direct cylinder with F&E in the attic above the new stove, to improve heat transfer and act as a heat sink. then take two pumped circuits from the cylinder: HWS coil and heating to the common heating header (oil-solid fuel header). A second f&e line to the oil boiler return should maintain correct operating pressures.

any thoughts on how effective these particular gravity loops are at delivering heat and if this proposal to improve efficiency would be really appreciated.
and thanks for taking the time to read through this

thanks

s

View media item 39579

 

[Norcon]

Page 18 and 19 are more typical of the set up using a neutralizer manifold.
http://tinyurl.com/cakjpdt

the gravity flow presently rises from boiler to attic and drops to the cylinder, before returning through the floor screed back to the boiler.

Sounds like a Dunsley "Up and Under " circuit you are describing.
Dunsley recommend an accelerator circuit due to the circulating pressure being very small.

 

[shagty]

Thanks Norcon

Thanks for your suggestions. A 4-pipe stove and accelerator circuit on the gravity circuit should eliminate the buffer/heat sink at attic level. I fogot to mention in my previous post that the attic is not large enough to accommodate the HWS cylinder but I cant see a problem with an accelerator.

As a matter of interest, what pump/flowrate and control temperature do you recommend for the accelerator? and would it be wise to use a injector tee one size up from the 28 line size?

And did you have any thoughts on the hot water priority control illustrated in the sketch attached: diverter velve in series with 2-port?

Thanks again for your help.

Regards S

 

[Norcon]

You can buy 28mm compression injector T's. They have a nicely tapered injector nozzle compared to a home made one.
I've only ever made one and it worked ok.
Regarding flowrate use the lowest flow to make it work. Hi-Lo stats are important also.
If you choose not to use a neutralizer then a nrv system can be used.
Just use two port valves for hot water priority. Much simpler wiring.

 

[shagty]

thanks again.

good point on the wiring!
is the objective of hi-lo stats to prevent cycling on the gravity accelerator?

regards s

 

[Norcon]

Page 17 explains the purpose of hi-lo stats for a typical boiler stove.
http://tinyurl.com/6xcte8y

 

[shagty]

Page 17 explains the purpose of hi-lo stats for a typical boiler stove.
http://tinyurl.com/6xcte8y[/QUOTE]

much appreciated.